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Comment by kazinator | Hacker News Reader

I would make a -$200 transaction whose breakdown with deductions and taxes and whatnot are all mirror images of the original $200. It exactly cancels the incorrect original transaction to zero across all accounts in the ledger. This is followed by the $50 is a new, independent transaction. No brainer to understand, or audit.

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In some situations this is ok. But if money actually changed hands then you can’t pretend you didn’t pay someone, so you’ve got to essentially create a debt or a new check, depending on whether the new total is negative or not. And that means all those new amounts may now need a different effective date. And each state can have different rules about collecting overpayments back from employees (some simply don’t allow it). We deal with staffing companies where folks forget to fill out Friday or fat-finger something on their timesheet, and we get it 2-4 pay cycles late, mixed in with other corrections and adjustments. There’s quite a lot of specialized logic involved.

I would say that all the additional complications make it even more imperative not to conflate the cancellation with the correction (another source of complexity into the mix), but do a clean cancel (as much as possible) followed by a reissue.

If there is any problem with the $200 cancellation, that has no effect on the correctness of the $50 reissue, which is entirely independent. It's easier to reason about problems with the $200 cancelation. Ideally, all affected accounts should be reimbursed as if the original never happened. If some account is debited $12.34 and then later credited $12.34, that's easy to match up and verify.

Obviously that’s the ideal situation. But in cases where you’ve already deposited funds you can’t pretend you didn’t.

I'm saying: do exactly what you would with the $150 offset, but use $200 to make it a complete offset. I don't see how it helps to work with $150 than $200.

That's what supermarkets do. They void transactions (usually needing a supervisor's approval) and then re-enter the purchase correctly.

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